PowerShell turning an if else statement to a Foreach Loop

I have a need to get rid of some users that do not exist in AD anymore but are still installed to an application, I have a script which provides a list of users and assigns them to a variable. At the moment I want a list of users that do notexist. This works for a single user:

#One user in an Application 

$Users = $repository.Users.FindAll() | where {$_.username -like "*johnsmith*"} | select username 

Username                                                                                                                                                                        
--------                                                                                                                                                                        

JohnSmith


#See if user exists in AD (Match Username with AD UserPrincipalName)

$users = $repository.Users.FindAll() |where {$_.username -like "*johnp*"} | select username 

$users2 = Get-ADUser -Filter "UserPrincipalName -eq '$($users.username)'" -Properties  LastLogonDate

if (!$users2 )
{
Write-Host "$users doesnt exist"
}

else
{
Write-Host "$users does exist"
}


> @{Username=JohnSmith} doesnt exist

Problem I am getting is feeding this to a foreach loop for multiple users in the variable. How can I put this to look through the object for each user and output the ones which do not exist?

#List of all users in Appication

$Users = $repository.Users.FindAll() | select username 

Username                                                                                                                                                                        
--------                                                                                                                                                                        

JohnSmith
JohnSmith1
JohnSmith2

Tried this, but doesnt work, shows all users exist even though JohnSmith doesnt exist as above:

$users = $location.Users.FindAll() |select username 

$users2 = Get-ADUser -Filter "UserPrincipalName -eq '$($users.username)'"

foreach ($users2 in $users){
if (!$users2 )
 {
 write-host "$users2 doesnt exist"
}

else
{
write-host "$users2 does exist"
}
}

PS C:\>
@{Username=JohnSmith} does exist
@{Username=JohnSmith1} does exist
@{Username=JohnSmith2} does exist