An important prerequisite to reduce the scope of the cardholder data environment is a clear understanding of business needs and processes related to the storage, processing or transmission of cardholder data. Restricting cardholder data to as few locations as possible by elimination of unnecessary data, and consolidation of necessary data, may require reengineering of long-standing business practices.
Documenting cardholder data flows via a dataflow diagram helps fully understand all cardholder data flows and ensures that any network segmentation is effective at isolating the cardholder data environment.
The adequacy of a specific implementation of network segmentation is highly variable and dependent upon a number of factors, such as a given network's configuration, the technologies deployed, and other controls that may be implemented. You should be validating the scope of your cardholder data environment as part of your annual PCI DSS assessment process, including validation of any network segmentation.
Article Number 1178