XMLHttpRequest cannot load https://differentSubDomain.example.com/myPHPScript.php. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://www1.example.com' is therefore not allowed access.

Handling CORS with php.php

<?php
$subject = $_SERVER['HTTP_ORIGIN'];
$subdomain1 = 'www';
$subdomain2 = 'www1';
$pattern = '/http(s)?:\/\/('.$subdomain1.'\.)?('.$subdomain2.'\.)?(example.com)$/';
$regexResult = preg_match($pattern, $subject);
if($regexResult)
{
    header('Access-Control-Allow-Origin: '.$_SERVER['HTTP_ORIGIN']);  
    header('Access-Control-Allow-Methods: GET, PUT, POST, DELETE, OPTIONS');
    header('Access-Control-Allow-Headers: Content-Type, Content-Range, Content-Disposition, Content-Description');
}
echo "Hi the browser has decided you're allowed to see this";