Chickens, like YOU and your friends who shed skin cells, cause almost all the dust in the coop and in your home. In a small space with six millions (or fewer chickens), you're going to have a boat load of dust. Get your chickens out of the coop; get yourself some dust masks, open every window, door, etc. in your coop; stand in the door with your electric leaf blower turned on high and watch what happens. Don't go all the way in until the air clears. Then blow the miscellaneous area that need more.