Takes a LOT of dry-ice! Works darn well, though. Remove seats and carpet/mat and load the stuff in there... When sufficient front has formed on bottom of car, smack with hammer and watch it fly! This will break loose under-mat tar pads too.

Heat gun and scraper is most common method. Wear protection as hot bits of tar are very sticky and make nasty burns.

Oven cleaner will also do it (but it takes a looooong time to work through all that tar!).

--
Mike!