Associating Style Sheets with XML documents

Is there any way to link XSL sheets with XML documents , so that the XSL sheets are loaded only when they have changed instead of every time the XML data is loaded

e.g. a xml document of the form  -

<?xml version="1.0"?>
<?xml:stylesheet type="text/xsl" href="list.xsl"?>

.....
will load list.xsl every time this document is loaded, even if list.xsl has not changed since the last invocation

many thanks for your help
--mayank