Title:IRON MAN#180 by Denny O'Neill (writer) and Luke McDonnell & Steve Mitchell (art)
Synopsis: The Enforcer is hired by Obadiah Stane (I think) to kill the Terminate. On route, a bag lady stops him. I think she asks for change, but regardless, she and the Enforcer have a brief heated exchange. The Enforcer brushes her off. She shoots him in the chest with a sawed off shotgun containing explosive bullets, which was hiding behind the bag and says "Justice is Served!"
Is it key to the Scourge story? Yes, the Enforcer was the first hit by a Scourge. Also, apparently the same Scourge, when captured by Captain America would tie the Enforcer into his bogus origin.
Is is key to the rest of the story in this issue? Marginally. I think the Termite was defeated in the same issue, and Stane was the main villain in Iron Man issues of the time.
Other comments: Evidently Scourge didn't know where the Enforcer was headed. Otherwise it would have made sense for him to let the Enforcer kill the Termite first, since the whole reason behind the Scourge operation is to off super-villains.