// initiate the memcached instance
$cache = new \Memcached();
$cache->addServer('localhost', '11211');
// get all stored memcached items
$keys = $cache->getAllKeys();
$cache->getDelayed($keys);
$store = $cache->fetchAll();
// delete by regex keys
$keys = $cache->getAllKeys();
$regex = 'product_.*';
foreach($keys as $item) {
if(preg_match('/'.$regex.'/', $item)) {
$cache->delete($item);
}
}