If the network had a way of knowing this, then this masternode would not be necessary at all. The masternode serves as a "trusted party" - the network trusts the masternode, so if the attacker gained control of the masternode, then how would the network know that the control of the masternode was overtaken?
There is a checkpoints chain. All checkpoints MUST follow this chain without exceptions, and even key owner can't violate this rule.
P.S. How much times can you ask the same questions? Read the topic and commit description.