Certainly! Here's a step-by-step guide to set up policy-based routing for your scenario:

### Step 1: Enable IP Forwarding

1. Edit the sysctl configuration file:
   ```bash
   sudo nano /etc/sysctl.conf
   ```

2. Uncomment or add the following line to enable IP forwarding:
   ```
   net.ipv4.ip_forward = 1
   ```

3. Save and close the file.

4. Apply the changes:
   ```bash
   sudo sysctl -p
   ```

### Step 2: Configure Policy-Based Routing

1. Create routing tables and rules for each domain.

   ```bash
   # Create a new routing table for foo.com
   echo "200 foo" >> /etc/iproute2/rt_tables
   
   # Add a route to the foo.com routing table
   sudo ip route add foo.com via 10.10.10.10 table foo
   
   # Add a rule to use the foo.com routing table for traffic destined to foo.com
   sudo ip rule add to 10.10.10.10 lookup foo
   ```

   ```bash
   # Create a new routing table for bar.com
   echo "201 bar" >> /etc/iproute2/rt_tables
   
   # Add a route to the bar.com routing table
   sudo ip route add bar.com via 10.10.10.20 table bar
   
   # Add a rule to use the bar.com routing table for traffic destined to bar.com
   sudo ip rule add to 10.10.10.20 lookup bar
   ```

### Step 3: Test the Configuration

1. Test connectivity to each domain from an external source to ensure that traffic is routed correctly.

### Step 4: Make Configuration Persistent (Optional)

1. Create a script to apply the routing rules on system startup. For example, create a script named `policy-routing.sh`:

   ```bash
   sudo nano /etc/network/if-up.d/policy-routing.sh
   ```

2. Add the following contents to the script:

   ```bash
   #!/bin/bash
   
   # Add routing tables and rules
   echo "200 foo" >> /etc/iproute2/rt_tables
   ip route add foo.com via 10.10.10.10 table foo
   ip rule add to 10.10.10.10 lookup foo
   
   echo "201 bar" >> /etc/iproute2/rt_tables
   ip route add bar.com via 10.10.10.20 table bar
   ip rule add to 10.10.10.20 lookup bar
   ```

3. Make the script executable:
   
   ```bash
   sudo chmod +x /etc/network/if-up.d/policy-routing.sh
   ```

4. The script will be automatically executed whenever a network interface is brought up.

### Notes:
- Ensure that the routing tables and rules are set up correctly. Errors can lead to misrouted traffic or network connectivity issues.
- Regularly monitor and test the setup to ensure it continues to function as expected, especially after system updates or changes to network configurations.

This guide should help you set up policy-based routing on your VPS to forward traffic based on domain names without relying on `iptables`. Adjust the configurations as necessary for your specific network setup and requirements.