Browser cache and form with $PHP_SELF

Using $PHP_SELF, I have a form that calls itself until the user gets all the input right. Each time the user corrects some field and resubmits, the browser builds a cache of pages, as you can see with the browser back button. Is there a way to make the browser clear the cache on every submission so the user cannot go back to any previous page? Seems like I've seen sites that do this, but I'm not sure how they do it. Egan