Most policies again will tell you your policy applies only to occurrences within the USA and Canada. No liability coverage will extend to Mexico because in Mexico automobile accidents are considered a criminal offense rather than a civil matter. If you are in Mexico and have an automobile accident and have not purchased through a licensed Mexican insurance company a policy, you may be jailed and may have your automobile impounded.
As a point of interest, many American agents close to Mexico are licensed to sell for bona fide Mexican companies, so get it before you cross the border and have happy memories of your visit.
Some insurance companies will extend your comprehensive and collision coverage into Mexico but only up to a limited miles from the border, generally 100 miles.