TL;DR
I can't speak for all INFJs (and I don't think it relates to type, as
@charlatan repeatedly said), but I am capable of grudges. It doesn't render me incapable of forgiveness and it largely depends on the person and the infraction. Forgetting doesn't work, because there will always come a time where you'll be reminded of the infraction and the grudge is revived. In some way it is a curse, but one that is most likely to affect you more than the one that is supposed to be hurt by it. In all likelihood, they don't even know of your anger towards you. You see them going by carefree, leaving you with more hatred than you actually started with. It changes the dynamic you could potentially have with that person had they ever been confronted with and acknowledged their infraction. If they don't see it, they can't know it. But then again, there are also people who don't see a problem with their infractions, even though they know of them and your feelings about them.
Both instances are cases where I really imagine to become physical, just so that they feel a fraction of the suffering they have caused me. Hatred is the easy way out, but the side effect is a coldness that spreads from there to other relationships as well. Basically, it infects your core self. Avoidance is the road to take if you want to forever wander in the dark. It's neither hatred nor forgiveness. It's cowardice, a fear of closure and the truth. Hatred twists the truth to pertuate the feeling, reinterpreting the situation in ever more nefarious ways to justify the amount of hatred you develop to that person, as the objective cause of your suffering. As such, hatred and avoidance are two different flavours of the same thing.
Forgiveness is hard. It takes the first step of confronting the other party, which is the most difficult thing to get going at all. But then you approach a new obstacle: listening and understanding, from both parties. You can try it, but this is where most attempts of forgiveness fail to come to pass. I haven't reached any part beyond that. Either the infraction was never big enough to take such radical effects, or I don't see anything happening any time soon with the other party, for one reason or another. One attempt at forgiveness had failed (that was back in secondary school), and I still hate that person for it. I also still hate my 4th grade teacher, which I was recently reminded of while walking past the school.
(There are other examples as well, but not any to be mentioned in public.) Therefore, I don't believe that forgetting is ever going to work, because the things I hold grudges for tend to mark me for life. Any other thing cannot be called a grudge in my book.