Upon receipt of a configuration BPDU with the topology change flag set, how do the downstream switches react?

Moving all ports to a blocking state is an incorrect reaction to a TCN; it would cause network disruption.

While flushing MAC addresses occurs, it's specifically 'old' or dynamically learned entries that are flushed to prevent blackholing, making 'all MAC addresses' less precise than 'all old MAC addresses'.

Temporarily moving non-root ports to a listening state is part of the STP state transition process, not the direct and immediate action related to MAC address table management upon receiving a TCN flag.

When a switch receives a Configuration BPDU with the Topology Change (TC) flag set, it immediately flushes out its dynamically learned MAC address entries (or significantly reduces their aging time) to ensure that traffic is not forwarded to outdated locations after a topology change.

Updating a 'Topology Change version flag' is not the primary immediate action for downstream switches regarding their MAC address tables in response to a TCN.