On a sealed unit, pull the cranks and manually turn the spindle. It should be smooth with no rough, grinding feel. If it's smooth, then it's likely OK. "Cleaning" in this case means to remove it, clean up both the threads on the BB and the threads in the BB Shell, lightly apply a bit of grease to the threads, and re-install.

Generally, you don't service these sealed units.

Another note; on the older non-sealed (cup and balls) type, you should always spring for new ball bearings.

They are cheap, and will prevent headaches. I've always disliked the term "repack", as it implies that you use the bearings again.
I use "rebuild" myself....