A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 16 February 2011
Can I still destroy the unit that Stone Guardian is in with A Stain Cleansed if I decide to pay for the whole unit? I believe I can, because the shugenja personality would be destroyed even if the guardian couldn't be. I'd just like to be sure.
Relevant text
A Stain Cleansed Text Battle: Choose your performing unbowed Magistrate and pay Gold equal to the target's total Gold Cost minus 2: Target an enemy card without attachments or an enemy unit. Destroy the targeted card or unit.
Stone Guardian Negate this card's destruction from other players' actions.
Zen Faulkes (rules official), 16 February 2011
Can I still destroy the unit that Stone Guardian is in with A Stain Cleansed if I decide to pay for the whole unit?
Yes. The action does not destroy the Stone Guardian, but that does not protect any other card in the unit.
http://rules.l5r.com/CE_Card_types#Attachments: "When a Personality leaves play, all his attached cards leave play in the same manner as he did. This leaving play is a rulebook effect contingent on the effect that took the Personality out of play, so the attachments are destroyed 'for' (as a consequence of) the original effect, but not 'by' the original effect."