Deleting all cookies probably means loss of all sessions. Worth a try.
I would like to be able to ensure that I've logged out of ALL sites that I've logged on to and might still be logged in on. Is there a way to do that without having to log out of each site individually, and without knowing all the sites' URL's? A script, an app, or a registry tweak?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic