It is my understand that the ASP.NET Cache is part of the w3wp process, meaning writing to and reading from it
(All in comparison to using ASP.NET Session State Server which does all these things)
Is this correct?
If you are refering to HttpContext.Current.Cache, then it will be part of the w3wp process. Caching of this form is stored in memory and do not require serialization.
It should not cross process boundaries, it will be a disaster if it does. That goes for marshalling too.