Scalability and elasticity are key capabilities to tackle the variable workload of a service. Cloud elasticity offers opportunities to manage dynamically the underlying resources of a service and improve its scalability. However, managing scalability of cloud-based systems may lead to a management overhead. Self-adaptive systems are a well-known approach to tame this complexity. In this position paper, we propose an approach for the continuous design and management of scalability in multi-cloud systems. Our approach is based on a three-layer architecture and relies on two existing frameworks, namely ScaleDL and CloudMF.