One jQuery Instance, Two Domains

I have two pages: a.example.com and b.example.com

a.example.com includes jQuery

a.example.com contains an iframe pointing to b.example.com

both pages have document.domain set to the same parent domain, example.com

How can I use the jQuery include from a.example.com to call $.ajax({ url: " b.example.com " }) from inside the b.example.com iframe?

In other words: Both pages can currently access the Javascript of one another, but I can not get the AJAX call to function without throwing XSS errors. That is, without including jQuery on b.example.com too. How do I avoid including jQuery twice?

Example of the contents of the iframe:

<script>

document.domain = "example.com";



function proxyAjax() {

   var jQueryParent = parent.$.sub();



   // Chrome gives error: XMLHttpRequest cannot load http://b.example.com/. Origin http://a.example.com/ is not allowed by Access-Control-Allow-Origin.

   jQueryParent.ajax({

      url : "http://b.example.com/",

      success : function() {

         console.debug("Success");

      }

   });

}



proxyAjax();

</script>