Fragment caching with touch (2.3.5)

Hi, I am working on an ecommerce shop. Currently we cache all the product thumbs using fragment caching with the product key and we expire the cache using Touch.

<% cache product do %> ... <% end %>

Now if I want to cache the product page, what key do I have to choose considering that I am already using the product key. And if I don't the product how am going to be able to expire the cache with touch?