This is a misunderstanding of Gresham's law which only applies for multiple currencies that are nominally of the same value. Meaning, if there is a $1 silver coin and $1 gold coin, everybody would be hoarding the gold coin and "getting rid of" the silver coin.

Also, a currency is not something you hoard, it's something you "get rid of" by giving it to someone else in return for goods and services. In your example, the "weak" currency would become the standard medium of exchange, while the "strong" currency would for all practical purposes disappear from circulation.