closing cavity under door threshold

I'm thinking about the little details about wall building, since I will be starting this after Christmas. New cavity wall built up to ground level minus 65mm (65mm left for screed to floor level), pouring floorslab inside, but how is the cavity closed under the door threshold, so that the solid floor stretches "over" the cavity ? (I will probably have the UPVC door sill set down a course so you don't have to step up and over it to get outside) And what happens to the floor slab DPM / wall DPC under the door ? Thanks, Simon.