<p>Satellite and 6G technology are deeply integrated to jointly build an "air, space, ground integration" network, laying a foundation for realizing truly full-area, full-time, full-scenario intelligent connected cars and autonomous driving. In the Internet of Vehicles (IoV), low-latency real-time inter-vehicle communication serves as a critical enabling technology for alleviating traffic congestion, reducing collision risks, and enhancing road safety. However, the open wireless communication nature of IoV imposes stringent privacy and security requirements. Current security protocols often fail to achieve true unlinkability of vehicular messages and lack adequate support for vehicle-to-vehicle (V2V) communication in multi-domain scenarios. To address these challenges, this paper proposes an unlinkable V2V communication protocol tailored for multi-service-domain environments. Our protocol introduces a hierarchical dynamic anonymization mechanism that decouples vehicle identity authentication from message verification. By dynamically assigning anonymous identities according to authentication levels, the protocol effectively ensures message unlinkability. Furthermore, the integration of smart contract technology enables efficient decentralized cross-domain verification of traffic-related messages. Notably, the proposed protocol stores only the local public keys of road-side units (RSU) on the blockchain. This design significantly reduces storage overhead by eliminating the need to store large volumes of vehicle-related authentication data on-chain. The security of the protocol is evaluated through both informal analysis and formal proofs within the random oracle model. Comparative performance evaluations against existing protocols reveal that the proposed solution exhibits lower computational and communication overhead.</p>