add_filter( 'woocommerce_add_cart_item_data', 'wdm_empty_cart', 10, 3);
function wdm_empty_cart( $cart_item_data, $product_id, $variation_id )
{
global $woocommerce;
$woocommerce->cart->empty_cart();
// Do nothing with the data and return
return $cart_item_data;
}