Current blockchain technologies provide very limited interoperability. Restrictions with regard to asset transfers and data exchange between different blockchains reduce the usability and comfort of users, and hinder novel developments within the blockchain space. As a first step towards blockchain interoperability, we propose the DeXTT cross-blockchain transfer protocol, which can be used to record a token transfer on any number of blockchains simultaneously in a decentralized manner. We provide a reference implementation using Solidity, and evaluate its performance. We show logarithmic scalability of DeXTT with respect to the number of participating nodes, and analyze cost requirements of the transferred tokens.