From the article:
"Zone Control
A player controls a zone if they control a creature in that zone and their opponent does not. Do not count Pests or Incapacitated creatures."
Like ACG said, this, this right here, is a reason to play Warlord. What an incredible tool. Enemies will have to actually guard their important Conjurations instead of leaving them behind, otherwise the Warlord may steal them. Can you imagine stealing a Mana Crystal or two with this? So sick. Well done AW, well done I say!