Help documentation about the Locate Change Sets editor is here https://jazz.net/help-dev/clm/topic/com.ibm.team.scm.doc/topics/t_locate_change_sets.html

In  addition to the 4.0 Locate Change Set editor, another way is to look at the work item that has the fix associated then see that it is "included in build", if you have a build on your stream. For example, you would know that it was delivered to the INT stream when it is shown as "included in the INT.rcb build" (for example).

During the end game, for maintenance streams, and whenever delivery is time sensitive, I will also add a comment to the work item saying that I delivered the change set to the stream.

There is an enhancement to help with this issue... see Story 93619: As a user, show me where my changes have flown.
https://jazz.net/jazz/web/projects/Rational%20Team%20Concert#action=com.ibm.team.workitem.viewWorkItem&id=93619

You could compare the two streams and see the differences. For something more specific, you'll have to go with Arne's suggestion of using the Locate Change Sets editor. If you're not on RTC 4.0, there is a basic locate change set action. It only works on one change set at a time and can be invoked from the change set context menu (ie. a work item in the links tab). With the action, you'll select the stream where you want to see if the change set exists there and you'll be told if the change set is in the selected stream.