I logged out of the Fitness.se site, cleared my cache and, look, I am on it but not logged in. Just to let you know the site is in private beta for two more days.
I click on meta not logged in, and I can still see the site.
You didn't actually clear your cache (both HTML 5 local storage and cookies) all the way. If you did, you would not have access.
When I log in with IE9, then
.. I indeed lose access to the private beta. You will too.