diff --git a/Doc/library/importlib.rst b/Doc/library/importlib.rst
index 65b63c8..9a11e0b 100644
--- a/Doc/library/importlib.rst
+++ b/Doc/library/importlib.rst
@@ -88,9 +88,12 @@
 
 .. function:: invalidate_caches()
 
-   Invalidate importlib's internal caches.  Calling this function may be
-   needed if some modules are installed while your program is running and
-   you expect the program to notice the changes.
+   Invalidate the internal caches of the finders stored at
+   :data:`sys.path_importer_cache`. If a finder implements
+   :meth:`abc.Finder.invalidate_caches()` then it will be called to perform the
+   invalidation.  This function may be needed if some modules are installed
+   while your program is running and you expect the program to notice the
+   changes.
 
    .. versionadded:: 3.3
 
@@ -119,6 +122,12 @@
         be the value of :attr:`__path__` from the parent package. If a loader
         cannot be found, ``None`` is returned.
 
+   .. method:: invalidate_caches()
+
+        An optional method which, when called, should invalidate any internal
+        cache used by the finder. Used by :func:`invalidate_caches()` when
+        invalidating the caches of all cached finders.
+
 
 .. class:: Loader
 
diff --git a/Lib/importlib/__init__.py b/Lib/importlib/__init__.py
index 50e9391..57fb284 100644
--- a/Lib/importlib/__init__.py
+++ b/Lib/importlib/__init__.py
@@ -1,23 +1,4 @@
-"""A pure Python implementation of import.
-
-References on import:
-
-    * Language reference
-          http://docs.python.org/ref/import.html
-    * __import__ function
-          http://docs.python.org/lib/built-in-funcs.html
-    * Packages
-          http://www.python.org/doc/essays/packages.html
-    * PEP 235: Import on Case-Insensitive Platforms
-          http://www.python.org/dev/peps/pep-0235
-    * PEP 275: Import Modules from Zip Archives
-          http://www.python.org/dev/peps/pep-0273
-    * PEP 302: New Import Hooks
-          http://www.python.org/dev/peps/pep-0302/
-    * PEP 328: Imports: Multi-line and Absolute/Relative
-          http://www.python.org/dev/peps/pep-0328
-
-"""
+"""A pure Python implementation of import."""
 __all__ = ['__import__', 'import_module', 'invalidate_caches']
 
 from . import _bootstrap
@@ -37,7 +18,15 @@
 
 # Public API #########################################################
 
-from ._bootstrap import __import__, invalidate_caches
+from ._bootstrap import __import__
+
+
+def invalidate_caches():
+    """Call the invalidate_caches() method on all finders stored in
+    sys.path_importer_caches (where implemented)."""
+    for finder in sys.path_importer_cache.values():
+        if hasattr(finder, 'invalidate_caches'):
+            finder.invalidate_caches()
 
 
 def import_module(name, package=None):
diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
index b3fda71..faa5830 100644
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -160,17 +160,6 @@
 
 # Finder/loader utility code ##################################################
 
-_cache_refresh = 0
-
-def invalidate_caches():
-    """Invalidate importlib's internal caches.
-
-    Calling this function may be needed if some modules are installed while
-    your program is running and you expect the program to notice the changes.
-    """
-    global _cache_refresh
-    _cache_refresh += 1
-
 
 def set_package(fxn):
     """Set __package__ on the returned module."""
@@ -768,7 +757,10 @@
         self._path_mtime = -1
         self._path_cache = set()
         self._relaxed_path_cache = set()
-        self._cache_refresh = 0
+
+    def invalidate_caches(self):
+        """Invalidate the directory mtime."""
+        self._path_mtime = -1
 
     def find_module(self, fullname):
         """Try to find a loader for the specified module."""
@@ -777,10 +769,9 @@
             mtime = _os.stat(self.path).st_mtime
         except OSError:
             mtime = -1
-        if mtime != self._path_mtime or _cache_refresh != self._cache_refresh:
+        if mtime != self._path_mtime:
             self._fill_cache()
             self._path_mtime = mtime
-            self._cache_refresh = _cache_refresh
         # tail_module keeps the original casing, for __file__ and friends
         if _relax_case():
             cache = self._relaxed_path_cache
diff --git a/Lib/importlib/test/source/test_finder.py b/Lib/importlib/test/source/test_finder.py
index 7b9088d..68e9ae7 100644
--- a/Lib/importlib/test/source/test_finder.py
+++ b/Lib/importlib/test/source/test_finder.py
@@ -143,6 +143,13 @@
         finally:
             os.unlink('mod.py')
 
+    def test_invalidate_caches(self):
+        # invalidate_caches() should reset the mtime.
+        finder = _bootstrap._FileFinder('', _bootstrap._SourceFinderDetails())
+        finder._path_mtime = 42
+        finder.invalidate_caches()
+        self.assertEqual(finder._path_mtime, -1)
+
 
 def test_main():
     from test.support import run_unittest
diff --git a/Lib/importlib/test/test_api.py b/Lib/importlib/test/test_api.py
index a151626..cc147c2 100644
--- a/Lib/importlib/test/test_api.py
+++ b/Lib/importlib/test/test_api.py
@@ -84,6 +84,34 @@
                 importlib.import_module('a.b')
         self.assertEqual(b_load_count, 1)
 
+
+class InvalidateCacheTests(unittest.TestCase):
+
+    def test_method_called(self):
+        # If defined the method should be called.
+        class InvalidatingNullFinder:
+            def __init__(self, *ignored):
+                self.called = False
+            def find_module(self, *args):
+                return None
+            def invalidate_caches(self):
+                self.called = True
+
+        key = 'gobledeegook'
+        ins = InvalidatingNullFinder()
+        sys.path_importer_cache[key] = ins
+        self.addCleanup(lambda: sys.path_importer_cache.__delitem__(key))
+        importlib.invalidate_caches()
+        self.assertTrue(ins.called)
+
+    def test_method_lacking(self):
+        # There should be no issues if the method is not defined.
+        key = 'gobbledeegook'
+        sys.path_importer_cache[key] = imp.NullImporter('abc')
+        self.addCleanup(lambda: sys.path_importer_cache.__delitem__(key))
+        importlib.invalidate_caches()  # Shouldn't trigger an exception.
+
+
 def test_main():
     from test.support import run_unittest
     run_unittest(ImportModuleTests)