How is it ensured that (computer) hardware (such as motherboards or processors themselves) does not suffer from from wrong signals due magnetic induction between wires?
Susceptible signals can be transmitted differentially. This means, if done correctly, magnetic fields can cancel on the wires and only relatively small levels of interference are received.
It works both ways. A data transmission using differential transmission produces less interference than one that is transmitted as a single wire and ground.
It's the same on telephone lines - back in the old days when telegraph poles used to carry the wires seperately, every few poles, the wires swapped positions to ensure that on a long run with other telephone cables, the net effects of magnetic coupling were very small. After this came twisted pair cable and even some ribbon cables actually use twisted pair.
Of course adding an outer earthed screen improves things (reduces electric field coupling) and the same applies to printed circuit boards. Buried (beneath and beside groung layers and tracks) transmission lines are quite common on some types of equipment.
Usually signal wires are alternated with a ground wire or ground plane on a data bus. Also transmission line theory is used to design high speed digital signal paths.