Yes, I have seen >100% scrubs.
It generally has to do with an active pool. Meaning newly written data is in a place, (directory tree), that has not yet been scrubbed. Thus, still needs to be scrubbed after the original amount of data was calculated. So, if you have 100GB to scrub, but write 10GB more, in theory you could end up with 110% scrub completion.
The other potential cause for the odd finish percent, is that the newish, (okay several years old by now), linear scrubbing mis-reporting the completion time / percent. The old method used to start at the top of the pool’s data structures and scan / scrub down. Using the new linear method is faster because it does not require as many hard disk seeks. And possibly fewer reads, since it can read adjacent data, but in different directory trees.
One other thing that can cause scrub completion times to be mis-reported is lots of small data blocks at the end of the scrub. Smaller data blocks take more time to scrub than larger data blocks, especially if they are fragmented around. Thus, you can sit at 99% complete for a long time, (like a hour or more), due to this issue.
So, nothing to worry about.