This is a followup task, generated from https://wikitech.wikimedia.org/wiki/Incident_documentation/20160126-20160126-WikimediaDomainRedirection#Actionables.
During a recent outage condition, operations had to perform multiple cache purges/bans. The actionables include better documentation of this procedure, as wikitech currently is somewhat lacking. Wikitech's info mainly comprises of: One-off purges - Don't do this. Consult a varnish specialist first. It also includes very limited info about varnishadm ban but not a detailed use case for our systems.