You cannot force a computer with a script to clear the history, only the user can clear their history, however, u can do 2 things that i know of:
1) Simply put some text saying "Please clear your browser cache before loggin back in since we update the site all the time"
2) Add the last updated device in the <head> tags, the browser will check the date against it's cached version and download the new one if its cache is out of date.
Any more experienced members, please correct me or suggest other alternatives if i'm wrong.
-DF
