Safari stores caches in a number of locations. There are cached items in com.apple.safari and then there are .cache files dedicated to Safari, such as the icon cache and the dedicated Safari cache (the first 23 bytes of which are basically the same). The Safari cache file holds NSURLRequest, which allows you to read a little extra data from it such as the creation date of the .cache file. So if you need to read this information in human readable format check out Safari Cache Reader by Black Bag Tools to extract the cached files. This can tell you when the last time a user reset their information and also let you check out the other content within them, which is much more in depth than simple History and icon cache data.
