f more dimensions are now automatically cached in the expensive object store.
  The expensive object store allows to cache such values between difference instance of integral objects that represent the
  same configuration. If integrals are created from an object (function or pdf) that live in a <tt>RooWorkspace</tt> the 
  expensive object cache of the workspace will be used instead of the global store instance, and values stored in the workspace
  store will also be persisted if the workspace is persisted