I would have liked to have broken this down issue by issue, but from memory the issues tend to merge together
Title: US AGENT#1-4 by Mark Gruenwald (writer) and _____ (artist)
Synopsis: A new Scourge (V) attends to kill the Matador, but seeing him no longer a criainal and with a wife and kids, gets cold feet. This Scourge turns out to be Priscilla (Vagabond) Lyons, and knowing that the Scourges will kill her for her failure, contacts US Agent for help. She tells him how she tailed Scourge IV and watched him kill a derelict (we never find out who this person was). Scourge IV goes after her (after first entering a theatre disguised as a patron and killing Blowtorch Brand) but is captured by US Agent. Scourge IV is killed by a higher up agent named Bloodstain, who now takes on the role of Scourge VII (another higher up named Caprice had become Scourge VI by this point). Caprice gets captured by USAgent. Soon after USAgent works his way to Scourge's headquarters, the mansion of ____ Halloway, who used to by the 1940s Agent.
We learn that the organization is run by Domino, having gotten Halloway to agree to fund the operation. During the final battle, Halloway is captured and Bloodstain and Domino are killed, though effectively shutting down the Scourge operation
Is it a key part of the overall Scourge storyline? Between the orgin of the organization and its shutting down, very much so
Does it tie into the main story in these issues? While the mini does reveal quite a few bits about USAgent's past, the story is largely about Scourge.
Comments: The Angel was relased due to lack of evidence, as revealed in Captain America#___
This was the last Scourge story to be written by creator Mark Gruenwald before Gruenwald's death. Fortunately for Scourge it revealed most if not all of Gruenwald's ideas regarding the organization and it can be said that he managed to finish the story he started many years earlier (beyond that annoying little Who the heck was killed in the flashback?).
The Scourge organization has not been seen since.