Google Public DNS’s methodology for countering cache poisoning attacks involves leveraging cryptographic techniques and carefully controlling the caching of responses. By ensuring that all data transmitted is encrypted and verifying the authenticity of each response, Google Public DNS mitigates the impact of malicious attempts to manipulate cached records. The service also implements rate limiting and IP blocking to deter abuse and prevent compromised servers from being used as attack vectors. Additionally, Google Public DNS employs a distributed architecture and load balancing mechanisms to distribute traffic and reduce the likelihood of a single compromised server affecting overall system integrity.