Is there a programmatic way to refresh / reset a preview icon in Finder?

Question

I noticed that while this applescript:

tell application "Finder"
  {...}
  update itm with necessity
  {...}
end tell

refreshes normal Finder icons, on the other hand, it doesn't refresh the Preview icons under Leopard. I'm wondering if there's an AppleScript / Carbon / Cocoa / C way to refresh or reset a preview icon of a Finder file. Do I need to explicitly communicate with quicklookd just to do so?

Thanks a lot.