Well, you asked.....you are wrong IMO. You have to think through how your erroneous conclusion could possibly come about.
You suggest that perhaps "NEC and Fujitsu have only licensed the majority of the MMP and have deemed ARM is responsible for the infringement of the 584 patent?". If NEC and Fujitsu benefited monetarily from the infringement of 584, they would be on the hook (along with ARM). IMO, the only way they could escape liability (placing such liability solely on ARM) is via a Patent Indemnification clause in all their purchase orders to ARM. But remember the nature of a Patent Indemnification clause: it is used in cases where no infringement is actually expected, but is insurance just in case infringement is later discovered. Thus, it is a "blanket" clause, covering any infringement of any patent in the product/service received from that supplier. Therefore, a scenario as you suggest simply could not happen IMO.
Hopefully this is sufficient explanation. I have wrote at length about this in past posts, but perhaps you missed it or chose not to read that particular "SGE Novel". To further clarify, Patent Indemnification clauses never ever specify a particular patent(s), for that would reveal that infringement was known at the time the contract was entered. From the supplier's view, would you identify the patent(s) you are indeed infringing in writing, knowing that there is some probability that this written word would be evidence that would "nail you" in future litigation? No way, unless your legal/contracts staff is incredibly stupid.
Hope this helps....
SGE