Your company runs a large-scale e-commerce application on Google Cloud, serving millions of global customers. The application consists of multiple microservices running on Google Kubernetes Engine (GKE) with an Istio service mesh for traffic management. The backend is powered by Cloud Spanner for transactional consistency, and BigQuery for analytics. Recently, users in different regions have reported inconsistent and stale data when querying order details immediately after placing an order. You suspect this is due to eventual consistency issues. What is the MOST effective way to ensure strong consistency while maintaining high availability across multiple regions?