You don't "clear the browser cache" from a web page (and fortunately for all of us browsing the web, you can't), but you can configure your server to send appropriate caching directives for the browser to follow.
…or you could move your resources so that existing cache directives known to your browser no longer apply (new URL, so it's not yet in the browser cache).
See http://www.gwtproject.org/doc/latest/DevGuideCompilingAndDebugging.html#perfect_caching