The only way I know of to force all browsers to ignore cache is to add some sort of unique identifier to the script tag.
One thing you could do is add a timestamp or version number via a GET param that won't mean anything to the server, or just change the filename of the script itself if that is feasible:
If significant changes have been made to the JS file though most browsers should be smart enough to fetch a fresh copy... you can also tweak your response headers if you have access to the server (cache-expire etc)
