Are you referring to a particular facility? Nikon calls their authorized shops Authorized Service Centers. This means that they've contracted with Nikon and have maintained the manuals, tools, and parts supplies that Nikon deems necessary. It does not mean they've completed training on all equipment.
As of June of this year they will be the only places in the US that will be able to perform most repairs, as Nikon USA has announced they will cease selling parts to independent shops(and dealers and the public) at that time. Unfortunately they have also started decreasing the number of ASC shops, or shops have been dropping them due to the cost of maintaining authorized status. This means shipping to a facility for most folks, even for a minor parts replacement. And it will be up to each shop to determine whether they are going to do 'partial repairs', Nikon Service doesn't.
As for sensor cleaning is concerned, there's no voodoo involved and the authorized shops are no more competent then the independents. Same goes for most repairs as well.