Use api Is there an API to force Facebook to scrape a page again?
$furl = 'https://graph.facebook.com';
$ch = curl_init();
curl_setopt( $ch, CURLOPT_URL, $furl );
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt( $ch, CURLOPT_POST, true );
$params = array(
'id' => '<update_url>',
'scrape' => true );
$data = http_build_query( $params );
curl_setopt( $ch, CURLOPT_POSTFIELDS, $data );
curl_exec( $ch );
$httpCode = curl_getinfo( $ch, CURLINFO_HTTP_CODE );