Hi,
Seemingly, you're talking about ability to ask server whether a new version of pages available.
To achieve that, please, try to enable "Check for newer versions of stored pages every visit to the page" in Run-Time Settings > Browser Emulation node.
In this case Vuser will send “If-Modified-Since” header in all relevant requests and in case there is no new content on the server it will respond with “304 Not Modified”.
Thanks,
Leonid.