Those types of Sigilyph will be running Magic Guard, so it will be immune to residual damage. But Whirlwind/Roar is your best bet, Meta651.Toxic or Whirlwind/Roar, probably. Toxic will either kill it with increasing damage if it tries to stay in, or force it to switch out to reset the Toxic damage and lose its stat increases. Either works. Whirlwind/Roar is a more direct way of eliminating those stat increases.
In addition, you can switch in a bulky Dark type (hello Tyranitar) and smash it before it gets too many boosts up. This one doesn't run the Flame Orb Psycho Shift, so your T-tar isn't afraid. Sigilyph will take some boosting before it really gets going.