the search results are held in a session variable:
$_SESSION["WADbSearch1_Products_Results"]
you can create a link to clear the results:
<a href="results.php?clear=1">Clear Search</a>
and create an if statement to unset the session based on the clear query string variable:
<?php
if(isset($_GET['clear']) && $_GET['clear'] == 1) {
unset($_SESSION["WADbSearch1_Products_Results"]);
}
?>