You're dealing with the EMI radiated from the motor. What you call reset is actually a reset after crash cycle which is triggered by a watchdog. There is no easy way to handle this. The real solution highly depends on your board and circuit design. The fastest solution can be moving your board away from the motor as far as you can, putting it in a metal case with case connected to ground and filtering the 220v input of your power supply.

Diodes and snubbers help reducing the EMI but not enough. You must protect your board against EMI interferences. Read the FAQ entry regarding EMI protection.