Sample using native ruby to only update information about hosts that were within the scope of the scan.

ip_inclusion.rb

#!/usr/bin/env ruby

require 'ipaddr'

# Hosts that we're already aware of by IP
known_hosts = %w{ 127.0.0.1 192.168.122.5 192.168.122.20 192.168.122.48
  192.168.122.134 192.168.122.200 192.168.122.210 192.168.122.230 }

# A new task has completed with the following target (only covers
# 192.168.122.0-192.168.122.127)
scan_target = '192.168.122.0/25'
new_host_list = %w{ 192.168.122.5 192.168.122.20 }

# This will hold the updated list of known hosts after processing
post_scan_result = []

# This could probably be a bit more efficient but it works as a proof of
# concept.
range = IPAddr.new(scan_target)
known_hosts.each do |host|
  if range.include?(host)
    post_scan_result << host if new_host_list.include?(host)
    next
  end

  # This host is outside of the scope of our scan
  post_scan_result << host
end

# This will only be missing 192.168.122.48
puts post_scan_result.inspect