Rubbing a note will invariably leave a mark that is at least as bad as the original ink stain because the rub mark is a smoking gun that something nefarious has been done to try to improve the note's appearance.
Having said that, you could try washing the note. Many old notes with manuscript (i.e., handwritten) countersignatures have had their ink lifted by washing, so if the stain is from old ink, it might lift right out without much effort. Goodness knows there are bank note washing experts who do this sort of stuff all the time, particularly in BC and Quebec. However, washing a note will likewise leave evidence of tampering, though many collectors can't tell the different between original and washed notes, and the act of washing could have a side benefit of improving the overall appearance of your note. Whatever you decide to do, just don't blame me if things go wrong
There's no sympathy for anyone who tries to wash/press/trim a note when things go wrong.