How create a parallel task to call the same method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApplication7
{
  class Program
  {
    static  void Main(string[] args)
    {
      RunIt();
      Console.ReadLine();
    }

    // This is so the individual queries can return both the status and 
    // something that identifies the input(s) that led to that succuss/fail
    private class Result
    {
      public readonly int Id;
      public bool Success { get; set; }
      public Result(int id)
      {
        Id = id;
        Success = false;
      }
    }
    static async void RunIt()
    {
      CancellationTokenSource cancellationSource = new CancellationTokenSource();
      CancellationToken token = cancellationSource.Token;
      // this List<int> values is the "proxy" for your set of server/domain
      // if in your case the servers & domains are independent vs. paired
      // then constructing the observableValues will be a bit trickier. :-)
      Random rand = new Random();
      List<int> values = Enumerable.Range(0, 10).Select(_ => rand.Next(1, 30)).ToList(); // ensure the values are "locked"
      Console.WriteLine("values=");
      foreach (var item in values)
      {
        Console.WriteLine(item);
      }
      Console.WriteLine();
      var observableValues = values.ToObservable();
      var tasks = observableValues.Select(x => Task.Run<Result>(() => {
        // This proxy for your validation "query" here just waits for the specified number of seconds, checking for cancellation each second
        // This is to simulate the queries each taking differing amounts of time
        Console.WriteLine("Start " + x.ToString());
        var res = new Result(x);
        for (int i = 0; i < x; i++)
        {
          if (token.IsCancellationRequested)
          {
            Console.WriteLine("Cancellation requested: {0}", x);
            return res;
          }
          Thread.Sleep(1000);
        }
        Console.WriteLine("Task = " + x.ToString());
        res.Success = (x & 1) != 0;   // Here the proxy for your validation success/failure is just that the input x is odd!
        return res;
      }, token));
      // by passing the token to the Task.Run() if cancellation happens before some Tasks get started, they just won't start at all

      // The Tasks don't actually start getting spun up until here:
      Result found = await tasks.Merge().FirstOrDefaultAsync(r => r.Success);
      cancellationSource.Cancel();
      Console.WriteLine(found == null ? "None found" : ("Found " + found.Id.ToString()));
    }
  }
}