diff --git a/IPython/core/interactiveshell.py b/IPython/core/interactiveshell.py
index a1c15bf..decdd07 100644
--- a/IPython/core/interactiveshell.py
+++ b/IPython/core/interactiveshell.py
@@ -1410,7 +1410,7 @@ class InteractiveShell(SingletonConfigurable):
         return [self.user_ns, self.user_global_ns, self.user_ns_hidden] + \
                [m.__dict__ for m in self._main_mod_cache.values()]
 
-    def reset(self, new_session=True):
+    def reset(self, new_session=True, aggressive=False):
         """Clear all internal namespaces, and attempt to release references to
         user objects.
 
@@ -1447,6 +1447,15 @@ class InteractiveShell(SingletonConfigurable):
 
         # Restore the user namespaces to minimal usability
         self.init_user_ns()
+        if aggressive and not hasattr(self, "_sys_modules_keys"):
+            print("Cannot restore sys.module, no snapshot")
+        elif aggressive:
+            print("culling sys module...")
+            current_keys = set(sys.modules.keys())
+            for k in current_keys - self._sys_modules_keys:
+                if k.startswith("multiprocessing"):
+                    continue
+                del sys.modules[k]
 
         # Restore the default and user aliases
         self.alias_manager.clear_aliases()
diff --git a/IPython/core/magics/namespace.py b/IPython/core/magics/namespace.py
index 0f232a7..2118d8f 100644
--- a/IPython/core/magics/namespace.py
+++ b/IPython/core/magics/namespace.py
@@ -491,6 +491,10 @@ class NamespaceMagics(Magics):
             we do a 'hard' reset, giving you a new session and removing all
             references to objects from the current session.
 
+        --aggressive: Try to aggressively remove modules from sys.modules ; this
+            may allow you to reimport Python modules that have been updated and
+            pick up changes, but can have unattended consequences.
+
         in : reset input history
 
         out : reset output history
@@ -533,8 +537,8 @@ class NamespaceMagics(Magics):
         such as the ipython notebook interface, will reset the namespace
         without confirmation.
         """
-        opts, args = self.parse_options(parameter_s,'sf', mode='list')
-        if 'f' in opts:
+        opts, args = self.parse_options(parameter_s, "sf", "aggressive", mode="list")
+        if "f" in opts:
             ans = True
         else:
             try:
@@ -552,7 +556,7 @@ class NamespaceMagics(Magics):
             for i in self.who_ls():
                 del(user_ns[i])
         elif len(args) == 0:                # Hard reset
-            self.shell.reset(new_session = False)
+            self.shell.reset(new_session=False, aggressive=("aggressive" in opts))
 
         # reset in/out/dhist/array: previously extensinions/clearcmd.py
         ip = self.shell
diff --git a/IPython/core/shellapp.py b/IPython/core/shellapp.py
index ee65d3a..c442658 100644
--- a/IPython/core/shellapp.py
+++ b/IPython/core/shellapp.py
@@ -331,6 +331,7 @@ class InteractiveShellApp(Configurable):
         # flush output, so itwon't be attached to the first cell
         sys.stdout.flush()
         sys.stderr.flush()
+        self.shell._sys_modules_keys = set(sys.modules.keys())
 
     def _run_exec_lines(self):
         """Run lines of code in IPythonApp.exec_lines in the user's namespace."""