The extreme pressures used in DI systems mean that a direct injector should never block, despite the build-up of combustion products.
If you have very poor quality fuel, some debris might build up on the injector filters, and the use a fuel additive with plenty of dispersants could possibly be helpful, by breaking up particles and re-suspending them.
In terms of in-combustion chamber carbon, then regular detergents whether a proprietary Mannich condensate or a poly-ether amine are likely fine. Poly-ether amine detergents are known to be ineffective for valve deposits, although some Mannich additives might be effective (there are some consortia of fuel additive manufacturers and car manufacturers looking to introduce minimum fuel specifications which include DI intake valve deposit buildup).
Some people (mainly additive vendors) have suggested that the addition of a fuel borne organometallic catalyst might be helpful by virtue of reducing soot formation. I worry a little bit about the use of organometallics in gasoline engines for reasons of spark plug fouling with today's ultra-long-life iridium plugs, and ash build up in the catalytic converters.
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