Your not actually supposed to multiply occlusion in like this. The thing is it sometimes works and does get pleasing imagery, but wrong nonetheless. This makes it really dangerous advice. So how are you supposed to use it then? That depends on what you model.
You could be modeling the ambient lightning, in which case you should add range your ambient color by occlusion. The ranging is done by multiplication of the ambient color of your surfaces than that is added to the reflection pass. In your image the occlusion works right for the floor but not much else. Its really important as just multiplying on top of tube for example leads to too dark interiors whereas its really only simulating the light of the sky/surroundings. Which is added with other lights.
You could be modeling dirt, in which case it is multiplied iwth the texture color, of ambient and diffuse but again not multiplied with reflections for example.
Or you could be doing reflective occlusion which is much harsher then its applied to the reflective channel but not interacting with the other parst of the image.
PS: misuse of ambient occlusion si number one reason for the very clearly cg look along with infinite depth of field.