diff --git a/IPython/nbformat/sign.py b/IPython/nbformat/sign.py
index e9e7adc..3280262 100644
--- a/IPython/nbformat/sign.py
+++ b/IPython/nbformat/sign.py
@@ -354,7 +354,7 @@ class NotebookNotary(LoggingConfigurable):
 trust_flags = {
     'reset' : (
         {'TrustNotebookApp' : { 'reset' : True}},
-        """Generate a new key for notebook signature.
+        """Delete the trusted notebook cache.
         All previously signed notebooks will become untrusted.
         """
     ),
@@ -383,7 +383,7 @@ class TrustNotebookApp(BaseIPythonApplication):
     flags = trust_flags
     
     reset = Bool(False, config=True,
-        help="""If True, generate a new key for notebook signature.
+        help="""If True, delete the trusted signature cache.
         After reset, all previously signed notebooks will become untrusted.
         """
     )
@@ -413,6 +413,9 @@ class TrustNotebookApp(BaseIPythonApplication):
     
     def start(self):
         if self.reset:
+            if os.path.exists(self.notary.db_file):
+                print("Removing trusted signature cache: %s" % self.notary.db_file)
+                os.remove(self.notary.db_file)
             self.generate_new_key()
             return
         if not self.extra_args:
diff --git a/IPython/nbformat/tests/test_sign.py b/IPython/nbformat/tests/test_sign.py
index 21b4f99..b0009f9 100644
--- a/IPython/nbformat/tests/test_sign.py
+++ b/IPython/nbformat/tests/test_sign.py
@@ -16,9 +16,9 @@ class TestNotary(TestsBase):
     
     def setUp(self):
         self.notary = sign.NotebookNotary(
+            db_file=':memory:',
             secret=b'secret',
             profile_dir=get_ipython().profile_dir,
-            db_file=':memory:'
         )
         with self.fopen(u'test3.ipynb', u'r') as f:
             self.nb = read(f, as_version=4)