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.
As a followup to this, viewtopic.php?f=59&t=100940&hilit=harsh+taskmaster+wide+valley
If the unit that was targetted by Harsh taskmaster while wide valley in play, but the personality is sent home. While he's at home during battle resolution, will the terrain effects apply to a unit at home?
Wide Valley's trait isn't restricted by location, neither by its own text nor by the rules. If it's a card on a unit and an action's effect tries to destroy it, Wide Valley will negate it. It may seem counterintuitive, but Terrain's effects aren't restricted to the battlefield where the Terrain is.