What happens when there is no entry in the Layer 2 CAM table that corresponds to the destination MAC address of an incoming frame?

Flooding across all VLANs would violate VLAN segmentation boundaries; unknown unicast flooding is always contained within the frame's own VLAN.

Switches perform unknown unicast flooding by sending the frame out all forwarding ports within the source VLAN to ensure the destination receives it. The ingress port is excluded to prevent the sender from receiving its own frame back, a behavior sometimes called split horizon at Layer 2. This is the standard Layer 2 unknown unicast flooding procedure defined in IEEE 802.1D bridging.

Dropping unknown-destination frames would break basic Layer 2 forwarding; the switch floods rather than discards because the destination may still be reachable.

Including the ingress port in the flood is incorrect because sending a frame back out the port it arrived on is unnecessary and would create redundant traffic toward the sender.