You'll see this accumulate at cluttered butcheries, kitchens and refuse stockpiles. The only sure ways to prevent it are making sure you have enough pots and barrels for food, haulers aren't overworked- if so, slow down your butchery- and you have tombs or available coffins for your dorfs so that they may be buried should they expire. Dorfs appreciate this particularly- the decay of a friend or relative will cause all but the most hardened dwarf to tantrum. Rock pots for food are invaluable, being lighter and more economic to produce than barrels, and ... *sighs* "nature friendly" if you feel like talking to the pathetic twigs that scurry about the surface, impregnating trees and generally mucking up the world with their "peace" and "not killing everything they see" and "manners."
If you dislike miasma around your butchery, exposing it to light will exempt it from the stench of decay- any tile exposed to the sky is considered "outside" and prevent the spread of the purples, even if it's just a 1 tile wide shaft through a thousand feet of solid rock. And remember, miasma can spread from any body part with 'meat' connected to it- so if you think you've cleared an area, a Goblin Lasher's Left Buttcheek may be behind a rock or stuck in a fortification stinkin' the place up.