If country A undercuts taxes below a set minimum of 15%, country B is within its rights not to recognize taxes payed in A for the purpose of avoiding double taxation. As a result, country B can demand tax payments on profits generated in B regardless of what taxes were payed in A. Unfortunately, in the real world governments are beholden to the commercial interests and rarely use the mechanisms available to them. Given enough willpower offshore tax havens can be eliminated in a split-second.