The full question that was recently asked was, "How do tokens issued on Factom prevent being double spent? Are those coins similarly limited in transaction capacity as the factoid is? Or do they reside in the entry credit chains?" Brian Deery, Chief Scientist at Factom responded with:
Brian Deery said:The clients will ignore any transactions that are illegal, like a doublespend would be. other types of transactions can be made illegal. For example, tether retroactively made these transactions illegal.
Coins built on top of factom would live inside one of the user subchains. The factom blockchain would just see them as data, and it would be up to clients to update their local state based on their own views of what is valid. It would be as scaleable as the rest of factom is.