I was needed to clarify several things on Hibernate according to my work (what is a query cache? does it have regions? what is update timestamps cache? does it have regions or not?)
In general, there is a lot of articles, papers, notes, manuals, etc. One of the excellent examples is http://tech.puredanger.com/2009/07/10/hibernate-query-cache/.
So we got some understanding on query cache and update timestamps cache after reading: there is a query cache with query and bound variables as keys and update timestamps cache, that keeps a record corresponding to each table (was it modified or not later than query result was cached).