@Override
    public void toData(DataOutput out,
        SerializationContext context) throws IOException {
      super.toData(out, context);
      out.writeBoolean(isPrimary);
    }
The reply to a PrimarRequestMessage, indicating if the sender is the primary
geode-core/src/main/java/org/apache/geode/internal/cache/partitioned/PrimaryRequestMessage.java