A distributed port scan operates by:

Blocking access to scanning clients is a defensive action taken by the target, not a description of how the scanning technique itself works.

Using denial-of-service software against TCP ports describes a DoS attack, which is a completely different category of attack from reconnaissance scanning.

Distributed scanning clients probe the target - they do not block access to it, as that would defeat the purpose of the scan.

In a distributed port scan, multiple coordinated hosts each scan a different subset of ports on the target, then their results are aggregated centrally. This approach keeps each individual source's scan rate low, making it difficult for intrusion detection systems to flag any single scanner as malicious based on volume thresholds.