Make use of the SetServerPageCacheDuration function, setting its parameter to 0 - insert the following markup in your XSLT function, for example right below <body>:
<f:function name="Composite.Web.Response.SetServerPageCacheDuration" xmlns:f="http://www.composite.net/ns/function/1.0">
<f:param name="MaxSeconds" value="0" />
</f:function>