Zchloty

A mention in The Colour of Magic says: "he selected a Zchloty leaden quarter-iotum" from "a handful of loose change plundered from a dozen realms". This suggests that the iotum is very low-value coin from an otherwise unknown domain called Zlocht or Zlochty.

The Discworld Companion confirms that Zchloty is a region, and that the corresponding currency is the iotum (pl. iota).

Annotation

The currency in Roundworld's Poland is the złoty, and there are other possible references to Poland in Discworld too. (See Sto Lat.)