Have the Scythians or Cimmerians invent the stirrup and composite bows simultaneously, adding a nomadic invasion to the mix. By coincidence they have an "ideology" more like the Dorians than to the Hyksos, Kassites or similar.
Invading the Hittites, Mesopotamia, and Egypt, the Scythians kill off the priests and literate classes in those civilizations and terminate contemporary literacy. Egyptian hieroglyphic script, and Mesopotamian cuneiform, are both forgotten. A new script is invented and the old scripts are indecipherable until linguistics or cryptography are invented. When the Mesopotamians, Egyptians, and Anatolians take control again over time, a lot of specialized knowledge that would have been carried into the Iron Age is, for at least a few centuries, lost.