Trusted Execution Environments (TEEs) enable secure code execution on machines that are not fully trusted by the user who runs the workload. However, existing TEE solutions mostly target CPUs and are typically tied to one specific instruction set architecture. Although some accelerators also provide support for TEEs, this leads to multiple, different TEE implementations on the same system, increasing its complexity and trusted computing base (TCB). This challenge becomes particularly apparent when workloads span heterogeneous processing units, because the diversity of TEE implementations complicates the creation of secure communication channels between the individual TEEs.