I'm not 100% sure regarding this plant's propensity to self-sow, but if it does, it never did it much for me. It does however, propagate by root cuttings, so digging up clumps that does not remove all the the roots, will not remove the plants from that area.

In any case, I would suggest the strategic and very selective use of a herbicide.

I agree with coolplantsguy.
I have geraniums selfsowing in many places. Where inappropriate I consider them weeds and pull them out. In lawns I use a spray bottle with a weedkiller.

To remove your particular geranium permanently in places, you have to dig it out with all its roots. I cut those runners back early until the mulch shows to keep a group of plants look neat.