Very random & unsubstantiated thoughts on “pepper spots” ...
We all remember the kid in Grade School that got a permanent mark from some kid poking him with a pencil? The pencil “lead” of course is graphite in some form of clay binder/matrix.
At any rate, once the graphite is deposited at a low enough layer of the skin (junction of the sub-dermis and dermis), this becomes a well-known mark called a tattoo!
The remnant of the lasered hair is probably carbon of some sort? If a large enough hair were lasered and left a carbon deposit at just the right skin layer … and the skin healed-over perfectly … would this also leave a virtual tattoo?
I do not know at all; as I said this is supposition. However, if you actually do have a tattoo-like deposit that deep in the skin, no amount of scrubbing is going to remove it. There could be, however, other options. Presumably your own body will “gobble up” the (organic) carbon and there could be ways to encourage this process. I can think of a few ways.