If the Foundation finds a portal or something towards the MGE world, their most likely steps are:
1. Set perimeter.
2. Try to use SRAs, XTACs, or any space-time stabilizing technology they have in attempt to destabilize the portal.
3. If it doesn't work, isolate the area and research. Anyone coming out of the portal instantly gets immobilized and captured for interrogation and study. No half-measures will be taken.
4. While a solution is still being worked on, they'll send expeditions via drones, Class-Ds and specialized MTF units to know more about the other side.
5. Find out about the situation and declare a Dominance Shift and Species Transmutation scenario and isolate the alternate world with as much automated defenses they could get. They did it in the Apotheosis canon (where most of humanity became superhumans, yet the Foundation still resisted the new world order), so it's not that ridiculous to assume they won't do it.
6. Research for a way to reverse the corruption process. If it fails, plan B is to find a way to shut the portal down for good.
Anyway, I just read SCP-008 (it looks like it's rewritten or something) after a very long time, and the containment procedures are read as this:
SCP-008 samples have been deemed Class V extreme biological hazards, and all related protocols apply. Incineration and irradiation measures will be deployed in the event of political or military action which may result in the facility being dismantled; a power failure; or zero communications from operatives or outside channels during any given eight hour period.
The quarantine period for operatives leaving the facility is four months. If a breach has occurred, incineration and irradiation measures shall be deployed. It should be the policy of all G2 sites to not prepare an evacuation procedure.
No evacuations. Incineration and Irradiation. Meaning no cure has been found so far. Also, the final paragraph in the article:
There is strong evidence to suggest SCP-008 itself did not form naturally on Earth, since variants of similar complexity would have displaced much of the ecosystem. In 1959, a short collaborative effort with the USSR to locate G2 sites and eliminate SCP-008 was negotiated following their discovery. The status of SCP-008 in Russian custody since collaboration ended is unknown.
Also, in the description:
Research into SCP-008 is highly classified and primarily aimed at preventing research which may lead to the synthesis of SCP-008 in the distant future.
The scary thing is, it's engineered can be replicated by current technology.
According to Addendum 008-1, only thing that can cure SCP-008 is SCP-500, and there are only 47 pills of it that the Foundation will never use unless necessary.
Hence, if we're looking at current containment procedures, in the case of a SCP-008 outbreak in a civilian area, the most likely scenario is that the Foundation, the GOC and the government in question will work together, lock the infected area down, kill and incinerate anyone trying to leave, drop a neutron bomb or two (for maximum irradiation effect) or just a couple tactical nukes (maximum heat and motserate irradiation effect), scour the area for any remnants and burn them down, then cover it up as a terrorist attack.
The Foundation is cold yet not cruel, but they know what should be done to prevent things from getting worse.