AP Grapher for Apple OSX is a great utility for scanning for wireless points, SSIDs and, for your own base stations, what security they are running.
But after a while it accumulates lots of old stations. You can reset the list and have it forget them and start again by deleting or renaming the file
~/Library/Application Support/AP Grapher/basestations.plist.
Restart AP Grapher and it'll start from fresh