The way that DataAssist works is through the trigger you specify. When this trigger is encountered the search values will be stored in a session variable. The search will show these results anytime that you browse to this results page without triggering a new search.
To clear a previous set of results you just need to trigger the search without any values specified.
What do you have the trigger setup as? Also, how would you like the user to reset the results to get back all of them? Do you want them to click on a show all button or something like that?