[Help] My Aussie went at my gf's parents Aussie's neck while he was sleeping

So my 2 year old Aussie was at my gf's parents house while we were gone today. They have been around each other on multiple occasions and play together and things of that nature. But while we were gone, My gf's dad said that my dog went over to their dog while he was sleeping and started biting him on the neck. Now I'm not talking about play biting his neck, I'm talking about he went for his throat to try and kill him, at least that's what I was told. This honestly terrifies me and he (my dog) will not be going back over there obviously. But I was hoping to get some help/advice on what steps I should be taking next to make sure that he doesn't do this to my mom's dogs since I am currently living with her. via /r/dogs http://ift.tt/2rIarhk