Get dns cache date from domain using C#

        [DllImport("dnsapi.dll",EntryPoint="DnsQuery_A")]
internal static extern UInt32 DnsQuery( [MarshalAs(UnmanagedType.LPStr)]string lpstrName, [MarshalAs(UnmanagedType.U2)]UInt16 wType, [MarshalAs(UnmanagedType.U4)]UInt32 fOptions,
            [MarshalAs(UnmanagedType.U4)]UInt32 t1, ref UInt32 prr, [MarshalAs(UnmanagedType.U4)]UInt32 t3 );

private class DnsInfo
        {
            public DnsInfo()
            {
                IPAddresses = new List<string>();
            }

            public string DomainName { get; set; }

            public uint TTL { get; set; }

            public List<string> IPAddresses { get; set; }
        }

        private UInt32 GetIP(Int32 ptr)
        {
            return ((NativeMethods.DNS_A_DATA)Marshal.PtrToStructure(new IntPtr(ptr), typeof(NativeMethods.DNS_A_DATA))).IpAddress;
        }


private DnsInfo GetDNSInfo(ref string strDomain)
        {
            var result = new DnsInfo();

            const int DNS_QUERY_CACHE_ONLY = 0x00000010;
            UInt32 ppQueryResultsSet = 0;

            if (NativeMethods.DnsQuery(strDomain, DNS_TYPE_A, DNS_QUERY_CACHE_ONLY, 0, ref ppQueryResultsSet, 0) == 0)
            {
                IntPtr ppr = new IntPtr(ppQueryResultsSet);

                NativeMethods.DNS_RECORD dnsrec = (NativeMethods.DNS_RECORD)Marshal.PtrToStructure(ppr, typeof(NativeMethods.DNS_RECORD));
                NativeMethods.NetApiBufferFree(ppr);


                result.DomainName = strDomain;
                result.TTL = dnsrec.dwTtl;

                var ip = new IPAddress(GetIP(ppr.ToInt32() + Marshal.SizeOf(dnsrec))).ToString();

                result.IPAddresses.Add(ip);

                var current = dnsrec.pNext;

                while (current != IntPtr.Zero)
                {
                    dnsrec = (NativeMethods.DNS_RECORD)Marshal.PtrToStructure(current, typeof(NativeMethods.DNS_RECORD));

                    // Skip over the header portion of the DNS_RECORD to the data portion.
                    ip = new IPAddress(GetIP(current.ToInt32() + Marshal.SizeOf(dnsrec))).ToString();

                    result.IPAddresses.Add(ip);

                    var old = current;
                    current = dnsrec.pNext;

                    NativeMethods.NetApiBufferFree(old);
                }

                return result;
            }

            return null;
        }