If someone registers YOURTRADEMARK.xxx, sue the ICM Registry.
It is the ICM Registry that creates the domain YOURTRADEMARK.xxx.
It is the ICM Registry that uses part of it's infrastructure to keep the domain YOURTRADEMARK.xxx online.
Without the cooperation of the ICM Registry the act of violating your trademark by registering a YOURTRADEMARK.xxx domain wouldn't be possible.
</not a lawyer 
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