package Foo;

use Moose;

has 'expensive_attribute' => (
    is  => 'rw',
    isa => 'Str',
    lazy_build => 1
);

sub _build_expensive_attribute { time }

sub do_stuff {
    my ( $self ) = @_;
    # Modify the core stuff here
    $self->clear_expensive_attribute; # From lazy_build
    sleep(2);
}

no Moose;
1;

package main;

my $f = Foo->new;

my $t1 = $f->expensive_attribute;

$f->do_stuff; # Invalidates attribute

my $t2 = $f->expensive_attribute;

# As expected, t2 contains the current result!
print "$t1 != $t2\n";