How do you start trusting someone again who harshly broke your trust ???

Is it really possible ?? Or will there be something in one's heart left for eternity.. something that will prevent the trust being 100% pure trust, but with some accompanying doubt deep inside. Is there a way one can LEARN to trust the person again, even if the person doesn't give clear evidence for being trusted again ??? What can be done, without involving the person to be trusted in achievement of this trust ??