Title: AVENGERS#263 by Roger Stern (writer) with John Buscema & Tom Palmer (artists)
Synopsis: Melter is observing Avengers Mansion through a view finder. He gloats to his assistant that he has a ray that will wipe out Avengers Mansion and everyone in it. But before he can fire the ray, the assistant guns himm down, declaring, "Justice is Served!"
Is it a key part of the overall Scourge storyline? No
Does it tie into the main story? No, beyond the fact that the Avengers are present in the mansion as a result of the main story. While the Melter's body was eventually recovered I believe, I don't know if the Avengers ever found out they were ever in danger.
Comments: This was probably Scourge's most significant hit
We never find out if the ray actually worked
From my memory, the assistant was merely tied up but someone else recalls that he was killed. Does anyone have a copy of the issue and can state one way or the other?