I am not aware of a way to do this from ePO. This has always been one of those things that you just had to have faith in.
If the Agent is functional (actively checking-in to ePO) and the task is applied at the proper system-tree location, it should be pulled by the client-node and enforced.
Now, there are ways to check after the fact.
You could run a report from ePO on Event: "1202: On-demand scan started (Info)"
If you were so inclined you could also check this on a random sampling of systems that should've received the task at the target system itself. You could do this by looking at the Agent log to see where the task was pulled, merged, enforced and subsequently added to the scheduler (assuming that you are unable to invoke the VSE console and view the managed tasks there).
Hope this helps.