IIRC they used the write-combining buffer, which was also a cache.

A common trick is to cache it but put it directly in the last or second-to-last bin in your pseudo-LRU order, so it's in cache like normal but gets evicted quickly when you need to cache a new line in the same set. Other solutions can lead to complicated situations when the user was wrong and the line gets immediately reused by normal instructions, this way it's just in cache like normal and gets promoted to least recently used if you do that.