"...was killed instantly"...lol. I can visualize the ragdoll after being crapped on by a troll because I've been crapped on by a couple of trolls after I ran out to lure them away from my build project. It happens to every one of us vikings at some point. That said, TangoBlue gets my vote for best response. You have to have a gap in your bench coverage somewhere. It's a pain in the azz, but look around and find it. I had a similar issue once before and just walked around with a hammer equipped until I found a spot where I couldn't build and found the gap that way. In fact, I found a couple of spots. Once patched up, I've never had another issue. If it was right outside your door, then the gap is prolly close by. I always build benches and stone cutters inside my stone walls all the way around so that nothing even spawns close to my wall or in the moat, and if damage is somehow done during the troll events, I can repair the wall without having to build any benches. Of course, it's also aesthetically pleasing to have them hidden, too. GLHF!
And God, please don't let them spawn in my living room!