The way I have handled this in the past is to do a process update to the dimensions followed by processing the latest partition in the facts. Then the final step would be a process default or a process index on the entire SSAS database. This ensures that all of your aggregations are processed correctly. This will increase processing time but will make sure that your query performance is as good as it should be (that is, if you have the right aggregations designed!).
More info from a Chris Webb presentation here: