For starters, there is a page on caching in the official Cocoon docs:
http://cocoon.apache.org/2.1/userdocs/concepts/caching.html
One piece of information which seems to be missing from that doc is that SourceValidity
is from the Apache Exalibur Source Resolving project with packages org.apache.excalibur.source
and its subpackages.
JX templates will be cacheable in Cocoon 2.2. There is information about caching JXTemplates in the "Advanced" section of JXTemplateGenerator.
There is information about caching XSP pages at XSPCachingWithCocoonHEAD.