There are cookies that exist that are not part of the browser. Even if you do a clear cookies from your browser of choice, these cookies still persist. these are cookies managed by adobe flash.
In an article mentioned here, a bunch of companies are being sued because of Quantcast, who basically recreated cookies using the flash system so that they could track users interactions with some big named sites.
So how do we remove those “zombie” cookies? Adobe provides a help page, but the page looks like its a demo when in reality it is your browser’s flash that you are controlling. The page of note is the web privacy one. You can go here to check it out.
What you will want to do is just do a delete all websites to clear your flash cookie cache. now you are back to being an anonymous user.