How to tell when the packUpdate loop is finished?

Ok, here's my problem.

I have a fire & forget variable. I want to set it on the server, then after it is updated to all ghosts through packUpdate, I want it to reset back to zero. My problem is, I don't know when the server has finished updating all ghosts. If I set my variable to zero in the packUpdate function, then some ghosts get the correct value, and some get a bogus value.

I've spent some time making some work arounds, but they are starting to not work so good and are a bit hacky, so I'd just like to do it the right away.

If anybody has any suggestions, that would be great!

Thanks,
- Drew