JLA/Avengers[]
The plot of this crossover involved Krona destroying a couple universes including the Antimatter Universe, and later attempting to use powerful artifacts from both DC and Marvel to drain and fuse DC's New Earth universe and Marvel's 616 universe in order to study Eternity and Kismet and learn secrets about how the new universe would begin. He was defeated and became sealed within a newly formed Cosmic Egg.
- First of all, the Cosmic Egg created during this event served as the main impetus for the 2008 Trinity series, and the events of JLA/Avengers were directly shown in issue 7.
- Second, JLA issue 108 directly shows the Antimatter Universe being destroyed and the Crime Syndicate figuring out that their history was erased and recreated.
In conclusion, Kurt Busiek's major writing role at DC allowed him to canonize his crossover event. Obviously it can't be used to scale between Marvel and DC, and for the purposes of DC Comics, the League simply visited a universe where everyone really looked like Marvel characters.
Green Lantern/Silver Surfer[]
This one is less concrete, coming from a direct reference to the crossover in Parallax: Emerald Night, where Hal mentions pursuing Cyborg Superman into another universe. Again, it's not possible to scale between companies, and for DC's purposes the DC characters simply went to a universe where everyone really looked like Marvel characters.