Brad, this header and some others to prevent caching are automatically output in the 4.7 version of OpenACS. Maybe someone wants to merge that back to 4.6, but as a new feature it first went into the development branch.
I wouldn't recommend the quick and dirty fix of putting that in the default-master for the standard toolkit, since it won't affect pages that don't use the default master, e.g. the search results page.
And that has nothing to do with caching of query results, it's just an http thing.
