That wasn't meant in a negative way. Just meant to imply...what do I do in the garage? Which the answer would be to clean it out also, and spray it too...I suppose.
Are the birds still in the garage? Do they have access to the garage? Do you store bedding in the garage?
If none of these apply, then I wouldn't worry too much. You can certainly mist the area where the chickens were kept with permetherin if you want. Just be careful if you have any cats that visit the garage as it's highly toxic to them.