[jQuery] Caching of javascript files

Hello,

If two sites, www.domainA.com and www.domainB.com both use jQuery and
allow script caching.
(sample tag <script src="/resources/jquery-1.3.2.js" type="text/
javascript"></script>)

In browser, in user's computer, will the two sites use the same copy
of jQuery (assuming both running same jquery version) ?

What if both domain use jQuery hosted on Google (http://
code.google.com/apis/ajaxlibs/) ?
Also, in this case if one site installs custom jQuery plugin, will it
be available to other site ?


Thank You.