questions regarding Journalling-FSes and w-cache reordering

I've got a question regarding the behaviour of w-caches with ATA-harddisks:
Is a ATA-harddisk allowed to reorder the operations from in w-cache ? On one side, this would be an opportunity to optimize head-movements (although a good cyclical-scan drive-scheduler would gain the same if it can rely on a linear sector-mapping), but on the other side, this would compromise the two-phase commiting of journalling FSes and render it useless. So I doubt that reorder- ing is allowed with ATA-HDs. Are my assumptions right ?